docs: def get_fragment_language() -> ParserElement:
      """Build a protein fragment parser."""
      _fragment_value_inner = fragment_range | missing_fragment(FRAGMENT_MISSING)
      _fragment_value = _fragment_value_inner | And([Suppress('"'), _fragment_value_inner, Suppress('"')])
      parser_element = fragment_tag + nest(_fragment_value + Optional(WCW + quote(FRAGMENT_DESCRIPTION)))
      return parser_element